Electron tube



Dec. 20, 1927. 1,653,544

H. A. BROWN ELECTRON TUBE Filed July 17 1922 3 sheets-Sheet 1 9 Jjgi v 3 A BE\ 20 1Q 5522? 9 MEQCgRY TBA 2 12 t I? ALKAL: vApo/a CONTENT TUBE CON UENTIONAL G45 CON TE NT TUBE IN ENSITY .UF SINGLE QESPONSE Dec. 20, 1927.

H. A. BROWN ELECTRON TUBE Filed y 17. 1922 3 Sheets-Sheet 2 Gigi} GRID VOLTA G55 I =QO Brown (Hi/gs maximum sensitiveness is that the vapor of Patented Dec. 20, 1 927.

UNITED STTATES 1,653,544 PATENT OFFICE.

HUGE ALEXANDER BROWN,

0] URBANA, ILLINOIS, ASSIGNOR T0 BOARD OF TRUSTEES OF THE UNIVERSITY OF ILLINOIS, 0F UBBANA, ILLDSIOIS, A CORPORATION OF ILLINOIS.

ELECTRON roan Application filed July 17, 1922. Serial no. 525,866.

My invention relates to electron tubes and the process of making the same.-

.For some time past I have .been enga ed in conducting experiments on electron tu es to determine the effect of different gases at varying pressures to yield the loudest signals when such tubes are employed for wireless telephony or the like. 7

I find that different gases have different ionizing potentials andthat hence, certain gases ma be employed with lower plate voltages t an others. a

After conducting a number of these experiments I conceived the idea of seeking a gas or vapor having a minimum ionizing potential whereby a lower plate voltage could be employed. My previous experience and knowledge of photo-electric cells indicated alkaline metals would give the desired result, namely, an atmosphere of a gaseous medium having a minimum ionizing potential.

I have discovered that commercial tubes may be filled with the vapor of an alkaline metal or metals and that thereby the per- .ormance of such tubes is greatly enhanced. Not only do they give a maximum output, that is. a maximum loudness of signals, for a relatively much lower plate voltage than do the devices of the prior art, but .they may in fact be used without any external source of potential in the plate circuit.

I have furthermore discovered that a tube constructed according to my invention has a greater range of sensitivity for the reception of signals than tubes as heretofore constructed. That is to say, not only is the in tensity of signal response greater in a tube of my invention, but also the range of late circuit potentials over which signals W1 1 be received is very extensive and the region of in tubes of the prior art.

I have further discovered that the conventional plate anode may be dispensed with and a coating of alkaline metal, either with or without a suitable metallic backing, may be employed instead.

The material which I employ is preferably the molecular alloy of potassium and sodium, that is to say, the elements potassium and sodium are combined in the proportion of their atomic weights.

I have employed the alloy of potassium an sodium above referred to on some tubes,

v this character extrem .sions as to the spacing of the electrodes.

not critical as it is for as much as twenty hours (normal life bemg 100 hours) without, so far as I can detect, any deteriorating eflect upon-the filament or any of the ot er parts of the tubes.

I am aware that mercury has been used as an atmosphere in tubes of this character. However, mercury apor makes a tube of e y critical, that is to say, 1t.makes it sensitive-at one particular value which is difficult to maintain. The ionization potential of mercury is, however, approximately twice that of the material which I have employed. I find the ionizatron voltage of the potassium sodium alloy which I have employed to be approximately four volts, Whereas, the ionization voltage of mercury vapor is approximately 10.5 volts. The employment of vapor of the potassium sodium alloy, instead of making the tube critical, has exactly the opposite effect, namely, it permits it to operate over a wide range of voltages' Tubes embodying my invention may be constructed by opening commercial tubes and introducing the vapor of the potassium sodium alloy, as I shall describe later in detail, or the tubes may be constructed as referred and filled with the desired atmosp ere during the manufacture thereof. If desired, the plate anode the coating of alkaline metal deposited upon the inner surface of the tube itself may serve the purpose of the plate anode. There are two types of tubes in which this invention is particularly useful, namely, in amplifying and detecting tubes such as the Radiotron and also in the so-called Mooreliead electron relay. which is of considerably larger dimeInn the latter the invention is of exceptional advantage.

In order to acquaint those skilled in the art with the manner of constructing and operating my invention, I shall now describe in connection with the accompanying drawings, one specific embodiment of the same.

Fig. 1 is a side elevational view of a commerclal electron tube having a glass stem sealed to the end of the-tube for introducing alkaline metal according to my invention;

Fig. 2 is a diagrammatic layout of the apparatus employed for evacuating the bulb and introducing the alkaline metal- Fig. 3 is a. chart showing a performance curve ofa tube constructed according to my may be dispensed with and with parts broken awa showing the manner in which the film of al ali metal is deposited upon the interior surface of the glass bulb of a conventional type of tube now in commercial use; and

Fig. 8 is a similar fragmentary sectional view indicating the manner in which the metallic alkali metal coating on the interior surface of the glass bulb may be employed instead of the plate .anode.

In producing a tube of my invention, I take the commercial tubes such as are on the market, for instance, the Radiotron manufactured by the General Electric Company, and introduce into the bulb thereof a potassium sodium alloy, this alloy being made in the proportions of the atomic weight of the two metals. The Radiotron comprises, as I have shown in Fig. 7, the base 1 which has p preferably four contacts 2 as is well understood by those skilled in the art, these contacts leading through a glass sealing stem 3 to the interior electrical parts, which parts comprise an oblong box-shaped shield 4 Which constitutes a plate anode for the plate circuit, this shield being supported by suitable wire supports 5 sealed into the stem 3 and one of the supports being electrically connected to a stud or contact 2 in the base 1. Within the plate 4 is,a coiled wire grid 6 which is mounted upon two supporting wires 7, one of which is connected through the stem 3 with a contact or stud 2 of the base 1. Within the grid '6 is provided the cathode filament 8 which is adapted to be heated to incandescence in the normal operation of the device. These parts are enclosed in the glass bulb 9 which has a sealing tip 10, as is well understood in the art.

According to the method which I now practice for producing a tube of my invention, I open the bulb 9 and attach thereto a hollow stem 11, as shown in Fig. 1, this stem being fused to the glass of the bulb 9 and having a stricture as indicated at 12 'for sealing oil", as will be explained later.

The stem 11 is connected by a net work of tubes, first to an evacuating mercury pump 13 through a. mercury tra) 14, which is maintained in a bath of liquid air-'15 in but this is immaterial.

order to prevent any mercury vapor from the pump 13 from getting into the bulb 9. A branch pipe 16 connects with a flask containin potassium pentoxid, this flask 17 being a apted to absorb any moisture which might be contained in the system. A stop cook 18 controls the connection of the pump 13 with the system of piping. Abranch' pipe 19 leads to a flexible hose connection 20, which hose connection makes a suitable joint with the container 21, which container contains a potassium sodium alloy. The container 21- is otherwise free of air or other gaseous media and it has a tip 22 projecting into the flexible hose coupling 20, this tip being adapted to be broken off to unseal the' container 21 to permit pouring of the potassium sodium alloy down through the tube 19 after the bulb 9 has been suitably evacuated. Thus after the tube 9 has been evacuated to substantial completeness, the tip 22 is broken 01f, thealloy 23 is poured down through the tube 19 and dropped upon the bottom of the connection with the tube 11 where it is heated as by means of the burner 25, the vapor of said alloy passing into the bulb 9 and condensing upon the walls thereof and upon the metallic parts and the scalingin stem. The vacuum pump 13 is left in operation during this heating by the heater 25 to maintain the vacuum. Incidentally, it carries ofi' some of the vapor of the alloy, The container 21 is provided with a constriction 24 whereby it may be sealed 011' by applying heat thereto after the alloy 23 has been introduced in suitable quantity into the system as described.

The filament of the tube may at this stage be heated to drive 011' the vapor or deposited metal, and thereafter the constriction 12 may be closed by heating as with the burner 25. If desired, the bulb 9 may first be sealed off by heating the constriction l2, and thereafter the filament may be heated to drive off the metal from the sealing-in stem and other metallic parts.

A coating of the potassium sodium alloy is thus secured upon the inner walls of the bulb 9, this coating 26 appearing in the shape of a metallic mirror. Not a great deal of the alloy is necessary to maintain the atmosphere of vapor. Variations in temperature, such as are caused by atmospheric variations, appear to have no appreciable etfeet upon the operation of the tube.

Instead of employing the plate anode 4:

as indicated, I may employ the lining 26 of potassium sodium alloy as the anode. In

this case, a wire terminal 27 is sealed in the side of the bulb 9 and it makes contact with the metallic lining 26. This metallic lining thereby serves the dual purpose of maintaining the atmosphere of vapor of an alkali metal, but also serves as the anode.

understood in all of I have conducted numerous tests upon the tube constructed as shown in Fig. 7, and I find that it has a performance curve of the character shown in Fig. 3. In the chart of Fig. 3, the X axis represents plate voltage, while the Y axis represents intensity of signal response, that is, rate of variation. The shape and character of the curve is substantially as indicated by the graph 30 having a maximum as indicated at 31, this maximum corresponding to substantially ten volts 1mpressedupon the plate circuit by an external source of current, such as shown at 32 in Fi 6.

It will be noted that the tube .of my in vention has' a relatively high intensity of si nal response over an extended range of pl ate voltage and as a matter of fact, the cell or tube will yield signals with no external source of voltage in the plate circuit. This is indicated in the chart of Fig. 3 by the fact that the graph 30 is continuous to the zero line.

The graph 32 shown in the chart of Fig. 3 indicates in relative proportion the characteristic of the conventional gas content tube, such as is now on the market. This type of tube has a very narrow range. That is to say, the impressed voltage upon the electrodes of the plate circuit must be mamtained very sharply at approximately volts. And if this voltage is varied in either direction, the intensity of signal response falls off very greatly.

The height of graphs 32 and indicates also the relative intensity of signal response for tubes of the prior art and for my tube.

The above statement as to optimum voltage applies to the Radiotron type of tube under discussion. In the case 0 the Moorehead relay tube, where the spacing between electrodes is greater I find that the voltage is around 25 volts.

Referring now to the chart of Fig. 4 which indicates the characteristics of a tube of my invention under different impressed plate voltages. it will be seen that I have plotted on the X axis the grid voltages, that is, the impressed signal voltages, and have plotted on the Y axis the resulting plate current, that is, the response to said variation, under different voltages. The graph indicated at 33 illustrates the character of the cell 0 crating on zero plate voltage. That is, Wit out an external source of current in the plate circuit. Graph 34 indicates the characteris-.

lie of the tube at 10 volts impressed voltage on the plate circuit electrode. Graph 35 indicates the characteristic at 20 volts. Graph 36 indicates the characteristic at volts. while graph 37 indicates the characteristic at from to 80 volts. It will be these charts that I am not indicating absolute values, but only relative values, and the shape of the curves optimum rather than the exact contour of the curves,

since thisnaturally will vary with individual cells, at least to some extent.

The dotted line curves 38 and 39 indicate the characteristic curves of tubes of the prior art withinthe narrow ran e in which such tubes are operative. It wifi be seen in each case that the tube of my invention has a better operating characteristic since the character of the curve on the negative side of the Y axis is of abetter shape, that is, nearer a straight line than the corresponding gas content or high vacuum tubes of the prior art. Particular attention is called to raph .34 where the zero voltage line crosses t e graph at a portion of the graph which is substantially a straight line on both sides of zero so that even if the grid is not maintained completely on the negative side the plate current which flows is substantially directly proportional to the variation in grid voltage for an appreciable distance in either the positive or in the negative direction.

The chart of Fi 5 indicates the sensitivity curve of a tu e constructed in accordance with my invention. I have shown here four graphs, namely, 40, 41, 42 and 43. These graphs represent the relation between grid potential and plate potential for a given value of current flow through the plate circuit. That is to say, the current flow through the plate circuit is maintained constant and the ratio between grid otential and plate potential is indicated y these curves. It will be noted that the major portion of the curves is a straight line indicating that the sensitivity is uniform over an extended period. In addition, the curves are relative y'steep, indicating a relatively high degree of sensitivity.

Graph 40 indicates the character of the sensitivity of the plate when the plate circuit current is of a value substantiall 4 milliamperes, while curve 42 indicates the ratio where the plate circuit current valve is substantially one-half milliampere. It will be understood that these curves are not drawn to absolute values, but are presented here merely to give the characteristics of the cell of my invention, that is, to indicate the contour and direction of actual curves which I have drawn from experimental data.

In Fig. 6 I have indicated the electron tube or cell of my invention as connected in a conventional receiving circuit for the purpose of receiving wireless telephone signals. The plate circuit in this case contains the telephone receiver 44 and a switch 45 which may be thrown to close the plate circuit through the battery 32 or through a connecting wire 46, which is merely a conductor for closing the circuit without an external source of potential. I find that this tube of my invention is far superior as a detector of damped or undamped waves, to high vacuum tubes or to inert gas content tubes. The tube also 'hasbetter characteristics as an amplifier than high vacuum tubes have. The maximum response is secured with an impressed potential of substantially-1O volts upon the electrode to the plate circuit, but the cell of my invention gives a response with no external source of current in the plate circuit.

According to the best explanation which I can give, this is due to the photo-sensitivity of the alkaline metal. I am not able to state definitely that this is the fact, and I beg leave to insert herein the correct theory of operation as soon as I am able to determine and formulate the same.

I assume that the film of metal which is in contact with the late anode 4 is photosensitiveto the lig t which emanates. from the incandescent filament 8 and that this photo-sensitivity is the source of internal potential for the plate circuit which is varied in accordance with the impressed grid potential. That is to say, the energy which creates the flow of current in the plate circuit apparently proceeds from ener 'y furnished y the battery 47, which battery maintains theincandescence of filament 8.

Whether an external source of light-will produce the same effect in the plate circuit I am unable to state. It, is known that in photo-electric cells such, for instance, as shown in Patent No. 1,381,474 issued to Dr. Jacob Kunz, the incidence of light rays upon the sensitive alkaline metal creates a difference of potential between the electrodes of the cell which may cause a current to flow independently of any external source of voltage.

A tube employed without an external source of battery in the plate circuit functions fairly well as a detector of damped or undamped waves.

This roperty of creating a flow of current in t ie plate circuit independently of an external source of current may be secured where the anode plate 4 is a separate plate or where it'isthe film of alkali metal.

Another feature of advantage which I have discoveredis that in both types of tubes above referred to the operation of the tube is enhanced by areduction of the filament temperature. I am unable to ex lain why this is true, but it is a fact esta li'shed by repeated experiments. The reduction in filament temperature means longer life of the tube.

I find that there is a further inherent advantage in the use of the alkali vapor and coating of metal.

In tubes of the above described "character repeated experiments show that the'gpresence of the alkali vapor will overcome and neutralize the efiect of the presence of residual gases due to incomplete pumping when the filament temperature is increased to about 10% above normal. The efiectiveness of the alkali vapor to perform this cleanup effect appears to depend upon the employment of ill h filament temperature. The use of rat er high filament temperature will cause a poorly evacuated tube to function as a high impedance and high voltage amplifier tube. This action increases the amplication constant at high voltage and smooths out the hump in the characteristic curve which occurs at low filament temperature in a poorly evacuated tube. I believe that the igher electropositive character of the alkali vapor" renders the union of the same with the residual ases relatively easy under the influence of igh'temperature of the filament. I cannot say definitely what the action is because I do not know, but I know that the efl'ect is secured under the condi-- tions stated and have proven the same by repeated experiment. I have observed that the characteristic curve of tubes which have been imperfectly evacuated improves in a manner which would indicate the disappearance of the gas.

It appears also that the'coating of alkali metal conserves the heat of the filament. This appears to be due both to the photo electric action of this coating, that is the conversion of some of --.,the radiant energy into electrical energy, partly to reflection and partly to the fact that this coating pre vents the radiation of'energy such as heat and light to the outside of the bulb.

While I have described the invention in connection with the conventional type of tube employin a hot metallic filament, I do not intend to limit the'invention to the particular tubes or the particular hot cathode above illustrated and described. The invention may be applied to such tubes as employ a hot cathode for excitin the action termed ionic or electronic bom ardment of the anode.

I do not intend to be limited to the precise details shown or described, nor do I intend to'belimited to the particular alloy which I have disclosed since other alkaline metals may also be employed and I intend to cover such gaseous materials for filling tubes of this character as would have ionizing potentials of five volts or less'.

I claim:

1. The method of transforming heat energy into electrical energy, which comprises heating a conducting body to the point of discharging electrons, discharging said electrons through an atmosphere of alkali metal mediate electrode'sealed in a closed bulb, and a charge of alkali vapor in said bulb, means to heat the cathode, an input circuit including a source of variable potential and said intermediate electrode, and an output circuit including said cathode, said ,anode and a translating device, said output circuit having no external source of potential.

3. Tn combination, an electron tube comprising a cathode, an anode, and an inter mediate electrode sealed in a closed bulb, and a charge of alkali vapor in said bulb, means to heat the cathode, an input circuit including a source of variable potential and said intermediate electrode, and an output circuit including said cathode, said anode and a translating device, said anode being maintained at a potential'difi'erence with respect to the cathode by the healing of the cathode.

4. In combination, a detector tube comprising an evacuated envelope containin a metallic filamentary cathode, a meta lic plate anode, an intermediate metallic grid electrode, an atmosphere of free alkali metal in the envelope,

an input circuit comprising a source of variable potential connected to the intermediate electrode, an output circuit including a means to heat the cathode,

translating device and anode being subjectedto a potential within the envelope by the heating of the cathode. 5. A detector tube of radio frequency waves comprising the combination of an enclosing glass bulb, a filamentary cathode adapted to be heated b current flow from an external source, a p ate anode, an interposed grid electrode and a permanent and stable filling of free alkaline metal, said detector tube being so organized as to exhibit a positive voltage upon the plate when the cathode is excited by heating.

6. A detector tu e of radio' frequency waves comprising the combination of an enclosing bulb of glass, :1 filamentary cathode adapted to be heated by flow of current from an external source, a plate anode, an interposed grid electrode, and a permanent and stable filling of free alkaline metal in said bulb, comprising the molecular alloy of sodium and potassium, said detector tube ing so organized as to exhibit a positive v'oltage upon'the plate when the cathode is excited byheating.

In witness whereof, I hereunto subscribe my name this 14 'th' day of July, 1922.

HUGH ALEXANDER BROWN.

said anode, said 

